1. Field
The following description relates to an image sensing technology, and more particularly, to an image sensing apparatus which senses visible images and far-infrared images.
2. Description of the Related Art
Image sensing technologies have been developed based on the spectrum of light that is visible to humans. Fortunately, the spectrum of light that is visible to humans can be sensed by silicon, which is widely used as a semiconductor material. However, research on infrared image sensors has also been conducted, to permit the viewing of objects when there is little visible light.
In the case of near-infrared rays, since they can be sensed by silicon, acquiring infrared images is not particularly difficult. However, since most objects emit little near-infrared rays at ordinary temperature, near-infrared rays are sensed from the light that is reflected from objects. That is, near-infrared images depend on the optical reflectivities of object surfaces. For example, since the surfaces of leaves reflect near-infrared rays very well, the near-infrared image of leaves will appear bright, while the near-infrared image of the sky will appear very dark since sky reflects little near-infrared rays.
Most objects viewed by humans emit a large amount of far-infrared rays at ordinary temperature, and, accordingly, research has been conducted on far-infrared rays. However, a specific sensor is needed to sense far-infrared rays, since far-infrared rays cannot be sensed by silicon. Far-infrared rays allow humans to view objects in dark places, and provide information about the temperatures of objects. One example is to acquire images using both a visible image camera and a far-infrared image camera and combine the images. Since the two cameras are not aligned on the same focus line, distortion appears in the combined image.
Further, images may be acquired using sensors and signal readout circuits. The images may then be combined using a digital signal processor (DSP). However, since two signal readout circuits and additional DSP signal processing are used, costs and power consumption are relatively high, and operating at high speed is difficult.